[Equest-users] How to properly model this 2-pipe FCU system in eQuest 3.65?

[David Eldridge]

The loop description sounds more like a "two-pipe changeover" system, which will be one of the choices in eQUEST....I see you've got a reply from John A. already with the details on that which should be helpful.

You'll have one FCU system per zone, although you may combine similar zones into one. (i.e. opposite faces of the building should be separate zones, at a minimum) OA quantity can be set to zero in the FCU dialog boxes, no problem there. The zones probably still have infiltration, and you might bump that up if there are operable windows. After simulating your can view the "summary" tab while viewing the air-side systems and you'll get a spreadsheet of all the AHUs, and a listing of capacities and outside air rates for verification purposes.

Your other obstacle is a little bit trickier. I think eQUEST must assume that there is some control valve - using three-way instead of two-way will give you the equivalent amount of pumping energy - i.e. constant flow.

However, one of the issues you may face is that if the coils are "wild" (no control valves, water flows all of the time when pumps are on) then there will be heat transfer with the room even when the FCU fans may have cycled off and eQUEST thinks the space temperature is met. In real life this might result in two circumstances depending on how much infiltration is taking place - actual temperatures go higher than desired, and/or occupants open their windows even in the winter.

You'll have to decide if those effects are important for your building, and if so you might have to adjust the eQUEST setpoints and infiltration rates to reflect what is actually happening in order to set a baseline. If the main concern is pumping energy instead of boiler energy and thermal comfort, then you should be fine using the three-way valves.

David



David S. Eldridge, Jr., P.E., LEED AP BD+C, BEMP, BEAP, HBDP
Grumman/Butkus Associates



From: Equest-users [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Amit Paul
Sent: Friday, December 05, 2014 11:21 AM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] How to properly model this 2-pipe FCU system in eQuest 3.65?


Hi everyone I'm trying to model an existing building in eQuest 3.65.

The building has a chilled water loop and a hot water loop (the same pumps changeover to pump HW in winter and CHW in summer).

All apartments have a non-ducted 2-pipe Fan Coil Unit. Nothing controls the coil (there's no 2-way valve), there's just a fan selector (LOW-SPEED/HI-SPEED/OFF), and there is no outside air being supplied to the apartments.

I'm struggling to understand how to properly model this in eQuest:

*         Should I create one HVAC SYSTEM (type FCU) per zone? Or one FCU system serving all of my zones? (Both seem to work, but I'm guessing there could be a drawback to using one versus the other)

*         What is the easiest way to ensure the outside air is zero?

*         How should I configure the FCU to mimic as closely as possible the (lack of) controls I have?

Thanks for any insight you can provide!

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